Variability in Pathologists' Interpretations of Individual Breast Biopsy Slides: A Population Perspective

Background: The effect of physician diagnostic variability on accuracy at a population level depends on the prevalence of diagnoses. Objective: To estimate how diagnostic variability affects accuracy from the perspective of a U.S. woman aged 50 to 59 years having a breast biopsy. Design: Applied probability using Bayes theorem. Setting: B-Path (Breast Pathology) Study comparing pathologists' interpretations of a single biopsy slide versus a reference consensus interpretation from 3 experts. Participants: 115 practicing pathologists (6900 total interpretations from 240 distinct cases). Measurements: A single representative slide from each of the 240 cases was used to estimate the proportion of biopsies with a diagnosis that would be verified if the same slide were interpreted by a reference group of 3 expert pathologists. Probabilities of confirmation (predictive values) were estimated using B-Path Study results and prevalence of biopsy diagnoses for women aged 50 to 59 years in the Breast Cancer Surveillance Consortium. Results: Overall, if 1 representative slide were used per case, 92.3% (95% CI, 91.4% to 93.1%) of breast biopsy diagnoses would be verified by reference consensus diagnoses, with 4.6% (CI, 3.9% to 5.3%) overinterpreted and 3.2% (CI, 2.7% to 3.6%) underinterpreted. Verification of invasive breast cancer and benign without atypia diagnoses is highly probable; estimated predictive values were 97.7% (CI, 96.5% to 98.7%) and 97.1% (CI, 96.7% to 97.4%), respectively. Verification is less probable for atypia (53.6% overinterpreted and 8.6% underinterpreted) and ductal carcinoma in situ (DCIS) (18.5% overinterpreted and 11.8% underinterpreted). Limitations: Estimates are based on a testing situation with 1 slide used per case and without access to second opinions. Population-adjusted estimates may differ for women from other age groups, unscreened women, or women in different practice settings. Conclusion: This analysis, based on interpretation of a single breast biopsy slide per case, predicts a low likelihood that a diagnosis of atypia or DCIS would be verified by a reference consensus diagnosis. This diagnostic gray zone should be considered in clinical management decisions in patients with these diagnoses.